The proposed investigation of the effects of cobra venom on hemostasis includes: characterization of the physicochemical properties of an anticoagulant we have purified from Naja nigricollis (spitting cobra) venom; resolution from, or proof of identity with, phospholipase; determination of the locus (loci) of action of the anticoagulant in the clotting scheme; preparation of antiserum against the anticoagulant; determination of the primary structure of the anticoagulant by sequencing techniques; study of the effects of modification of the protein on its anticoagulant activity. We expect to gain detailed basic information from these studies about the interaction of the anticoagulant with the clotting system. The components of the venom responsible for inhibition of platelet aggregation and inhibition of clot retraction will be isolated and the requirements for these effects will be clarified. A plasmin inhibitor from N. nigricollis venom, which has been partially purified, will be characterized, and its mode of action investigated. These proteins have the potential to provide new information about structural requirements of anti-thrombotic agents. As specific inhibitors, they should be valuable research tools in the study of the various elements of hemostasis, thrombosis, and their regulation, and should lead to new knowledge in these areas.